A wide variety of header systems have been developed for exhausting combustion gases from the cylinders of internal combustion engines and directing the gases to an exhaust pipe in order to improve horsepower, vary the maximum torque band and improve fuel efficiency of the engine. Basically, a header includes a flange plate that bolts up to the engine's exhaust ports, primary tubes that extend from holes in the flange plate at the exhaust port locations to a collector tube which collects the exhaust and directs it into the exhaust pipe having a muffler, catalytic converter, etc.
In the past, automobile manufacturers have provided cast iron header manifolds because they are easier to manufacture and emit less noise. However, these header systems provided less than ideal emission control and gas milage, so that tube-type headers are now provided on many new production cars. After market tube-type headers have long been offered both for improving street performance and for racing.
A variety of header designs have been developed. The most common is the 4-into-1 design in which four primary tubes from the flange to a collector or transition pipe where the total cross sectional area of the primary pipes is collected and reduced to the cross section of the exhaust pipe. In other designs, pairs of primary pipes are brought together, then the combined primaries are brought together in a collector. In pure race cars, the primary pipes from the flanges may be brought outside the vehicle independently, functioning as individual exhaust pipes. In other designs, primary pipes from opposite banks of a V-8 or V-6 engine may be brought together in a selected configuration.
Each of the header components has an effect on performance. For example, using a smaller primary tube diameter tends to lower the torque peak, which is advantageous in a street vehicle but not in a full race car. Longer primary tubes also increase low-end torque, as will a larger collector. Equal length primary pipes assure that each cylinder is scavenged equally. Uniform flow and avoidance of turbulence in the primary pipe, collector and exhaust system are important in reducing back pressure and maximizing both power and fuel efficiency.
The point where the primary pipes come together and enter the collector has been found to be a problem area in assuring smooth, non-turbulent exhaust gas flow through the collector. The cross sectional area of the combined primary pipe ends transitions through the collector to the (generally smaller) exhaust pipe cross section. The cross sectional area that is formed between the bundled primary pipe ends, approximately square with four primary pipes and approximately triangular with three primary pipes, is a major cause of turbulence.
Attempts have been made to smooth this transition by cutting back the adjacent surfaces of adjacent primary pipes, then welding them together to substantially eliminate the area between the pipe ends. This is difficult, expensive in design and manufacture, and with a number of complex welds may actually add to turbulence in this transition region.
Thus, there is a continuing need for improvements in header design to reduce or eliminate turbulence caused by the joining of adjacent primary pipes at the collector and transitioning to the exhaust pipe diameter.